One method of distance-measuring-devices is the measurement of the distance to an object by determining the time of flight of a light pulse. It is known in the art to provide distance-measuring-devices which send a precisely timed light pulse toward an object and to make gated measurements of the light reflected thereby. The time of flight of the light pulse is simply related to the range of the object through the relation d=c*Δtd/2, where d is the distance to the object, c stands for the velocity of light in the medium through which it propagates and Δtd is the time delay between the pulse emission and its detection.
Several distance-measuring-devices that include time-gated detection schemes are known in the art. As a well-known solution, a distance-measuring-device sends a light pulse toward an object and records the reflected light from the object by a light sensor (typically which converts the incident light to voltage/current) using two gated time-intervals equal of time. The light pulse emitted from a light source is typically driven by a pulse generator providing a digital pulse. A first gated time-interval is typically synchronized with the digital pulse such that it starts at the same time the digital pulse starts and another gated time-interval starting at the end of the digital pulse. The durations of both gated time-intervals are generally set to be equal to the length of the digital pulse. The range of the object is in one type of method is determined by the ratio between the amount of reflected light received during the first gated time-interval and the sum of the two amounts of reflected light received respectively during the first gated time-interval and the second gated time-interval.
The existing distance-measuring-devices are not accurate enough for security applications such as safety functions of automotive applications. Synchronization of digital pulses generates error. Furthermore the pulse length variation and delays are introduced which vary with environmental parameters such as supply voltage, temperature, or variation in electronic component parameters which drift from their nominal values. Solutions such as a calibration table stored in a memory of a distance-measuring-device exist. However, those solutions do not fully compensate the existing variations. Those solutions cost time, effort, and money for implementation.